not sure i seem to only get them from the group dungeon one

Same thing happened to me. Hollowjack didn't drop tickets. I also did it first thing, no tickets. None from Delve boss either. Next killed a World Boss and got the tickets.

Did you get a golden coffer from the delve, or just a purple one? I'm wondering that if perhaps Lord Hollowjack doesn't drop tickets at all, and maybe drops the same kind of gold coffer as you get in a delve, maybe that prevents you from getting your tickets and gold delve coffer when you kill a delve boss afterward?

I haven't even attempted Lord Hollowjack yet, but I did notice something else weird-- I got two different gold coffers from a delve, and possibly from a public dungeon as well.

It happened in the Ashalmawia delve in Vvardenfell where you stop the Daedric summoning rituals. There are apparently two different bosses in that delve-- the titan Phobbiicus (which is required for "clearing" the delve) and the Dremora Zylara. Killing both of them (in the same run) gave me two different gold coffers. I'll do it again later tonight to verify.

[Edit: When I did Ashalmawia tonight on PC EU, Phobbiicus didn't drop a coffer at, just some gold. Then I killed Zylara and got a gold coffer that said "Public and Sweeper." When I killed a public dungeon boss later, all I got was a purple coffer; and when I killed the boss in another delve, I got a gold coffer for "Delve." My guess is that maybe players submitted bug reports about Ashalmawia, but instead of removing the gold coffer from Zylara, they removed the gold coffer from Phobbiicus, the actual delve boss.]

And I think it also happened in the Rulanyil's Fall public dungeon in Greenshade, when I killed one of the regular bosses and then killed Hergor the Fallen in the group event. But I'll have to double-check later.